1. Field of the Invention
The invention relates in general to an optical device, and more particularly, to an optical device utilizing a periodic dielectric structure.
2. Related Art of the Invention
In recent years, photonic crystals have attracted many research workers by its excellent manipulation for photons. A variety of effects on photons by photonic crystals is caused by the structures and materials of the photonic crystals. Photonic crystals are periodic optical materials, e.g., periodic dielectric materials. The characteristic defining a photonic crystal structure is the periodic arrangement of dielectric or metallic elements along one or more axes. Thus, photonic crystals can be one-, two-, and three-dimensional. Most commonly, photonic crystals are formed from a periodic lattice of dielectric material. When the dielectric constants of the materials forming the lattice are different (and the materials absorb minimal light), the effects of scattering and Bragg diffraction at the lattice interfaces control the propagation of optical signals through the structure. These photonic crystals can be designed to prohibit optical signals of certain frequencies from propagating in certain directions within the crystal structure. The range of frequencies for which propagation is prohibited is known as the photonic bandgap.
In general, photonic crystals are provided for controlling the propagation and the intensity on the propagation direction of the light. A variety of devices constructed by photonic crystals had been studied such as waveguides, filters, multiplexers and optical fibers etc. Low loss, small size, and ingenuity are the main advantages of photonic crystals.
An important purpose of photonic crystal is beamsplitter. To divide the input power identically, many kinds of beamsplitters have been proposed, such as T-type, Y-type and cross-type photonic crystal beamsplitters. Referring to FIGS. 1B to 1D, schematic drawings of conventional T-type, Y-type and cross-type photonic crystal beamsplitters are illustrated respectively. Nevertheless, the conventional beamsplitters are either one input and two outputs or one input and three outputs, and a photonic crystal with at least two inputs and at least two outputs, e.g., a beamsplitter used in a Mach-Zehnder interferometer has become more and more important. Referring to FIG. 1A, a beamsplitter 100 used in a Mach-Zehnder interferometer is shown, in which the light may be input from the ports 102, 104, and output lights can be obtained simultaneously at the ports 106 and 108. Moreover, the light also can be input from the port 102 and 104 simultaneously, and output lights can be obtained simultaneously at the ports 106 and 108. Therefore, a photonic crystal beamsplitter with at least two inputs and at least two outputs is provided in this invention.